The present invention relates to a method of preparation of a water based epoxy resin curing agent in dispersion form which is formed by combining an amine-functional dispersion (A) with an amine-functional curing agent (B). The invention also relates to the curing agent obtained from said method, its use for curing two component water based epoxy systems, compositions obtained from such curing and various uses of the compositions obtained.
Epoxy curing agents in emulsion or dispersion form are well known in the art. For example, EP 0 637 324 (Klippstein, Air Products) describes hardeners or curing agents in the form of aqueous emulsions of active amino group-containing adducts made from an aqueous amine solution and an epoxy resin of a molecular weight greater than 700. The examplified curing agents, however, have viscosities above 500 mPa·s, and a pot life of less than 360 min.
U.S. Pat. No. 6,013,757 (Corley, Shell) describes the preparation of aqueous dispersions of polyamides that are used to cure liquid or solid epoxy resins. Polyamide curing agents are prepared from dicarboxylic acids and aminoalkylpiperazines that are dispersed in water to yield an oil in water emulsion.
EP 0 951 494 (Ghosh, Shell) describes the preparation of waterborne curing agent dispersions formed by the reaction of phenolic acids, a functional surfactant and an amine to form solid aryl amidoamines or solid aromatic glycidyl esters that optionally can be further reacted with a capping agent. Water is added under shear and phase inversion to yield an oil in water emulsion.
None of these reference provides for a curing agent for liquid epoxy resins which exhibits a low curing agent viscosity of less than 500 mPa·s, provides a long pot life of at least 360 min. and at the same time provides the ability to apply high solids coatings with liquid epoxy resins in combination with the required compatibility to yield transparent high gloss coatings. It is the object of the invention to overcome these and other drawbacks of the prior art.